Effective Biosorption of Nickel(II) from Aqueous Solutions Using Trichoderma viride

e primary objective of the present study is to evaluate the optimization conditions such as kinetic and equilibrium isotherm models involved in the removal of Ni(II) from the aqueous solutions by Trichoderma viride. e biosorbent was characterized by FTIR and SEM. e optimum biosorption conditions were determined as a function of pH, biomass dosage, contact time, initial metal ion concentration, and temperature. e maximum Ni(II) biosorption was obtained at pH 4.5. e equilibrium data were better �t by the Langmuir isothermmodel than by the Freundlich isotherm.e kinetic studies indicate that the biosorption process of the metal ion Ni(II) has followed well the pseudo-second-order model. e sum of the square errors (SSE) and chi-square (χχ) tests were also carried out to �nd the best �t kinetic model and adsorption isotherm. e maximum biosorption capacity (qqmm) of T. viride biomass was found to be 47.6mg/g for Ni(II) ion. erefore, it can be concluded that T. viride biomass was effective and low-cost potential adsorbent to remove the toxic metal Ni(II) from aqueous solutions.e recovery process of Ni(II) from T. viride biomass was found to be higher than 98% by using 0.25M HNO3. Besides the application of removal of toxic metal Ni(II) from aqueous solutions, the biosorbent T. viride can be reused for �ve consecutive sorption-desorption cycles was determined.


Introduction
Metal pollution has been a great concern for the past few decades.It is believed that the wide use of man-made chemicals, anthropogenic lifestyle, and rapid industrialization is the major source of metal toxicity [1].Nickel is well known as a heavy metal pollutant, present in effluents of electroplating industries, smelting, and alloy manufacturing, mining, and re�ning industries [2].According to WHO, the permissible limit of Ni(II) in drinking water is 0.5 mg/L [3].e non-biodegradable and bioaccumulating properties of heavy metals may pose serious threats to living organisms, [4].It has been reported that both occupational and environmental exposure to trace metals affects almost all compartments of animal systems including human health [1].In humans and animals, nickel is an essential micronutrient [5] because of its importance in the metabolic pathways.Nickel is one of the cofactors for urease enzyme in plants [6].ough, it is an essential micronutrient and/or cofactor, nickel is one of the heavy metal toxicants at higher concentration and is a well-known human carcinogen [7].Nickel has been implicated as an embryotoxin and teratogen [8].e higher concentration of Nickel causes dermatitis, nausea, vomiting, behavioral, and respiratory problems in addition to cyanosis, gastrointestinal distress, and weakness [9].All these biological disorder consequences alarm the need of nickel removal from the environment and to bring up its levels below the threshold limits from its sources.e classical physicochemical methods are commonly used for the removal of nickel from the industrial effluents, namely, evaporative recovery, �ltration, ion exchange, and membrane technologies.ough they are promising to some extent, but these processes have high reagent or energy requirements and generate toxic sludge that requires careful disposal [10].Furthermore, insufficient removal of traces of heavy metal ions, varying performances, and also high operating costs has limited the use of conventional physicochemical methods.us, there is a need for alternative methods for better efficacy with low cost and complete removal of toxic metals from the water bodies.
In recent years, the exploitation of eco-friendly biosorption technology using inactive and dead biomasses to detoxify metal-contaminated effluents in the aquatic environment is gaining importance day by day [11,12].Moreover, the biosorbents have high speci�c metal binding ability in complex media in contrast to carbonaceous sorbents which tend to adsorb metal ions in a nonspeci�c manner.ese advantages make biosorbents an economical alternative to commercial activated carbons in the removal of heavy metalpolluted water bodies [13].
e application of fungal organisms in the �eld of biosorption technology has become a part of active research by the environmental scientists.Fungal organisms like, Aspergillus niger [14], Streptomyces noursei [15], Pseudomonas aeruginosa [16], and Rhizopus arrhizus [17] have been reported for removal of heavy metals, such as Pb, Cd, and, in particular, Ni(II).Among the fungal organisms, the T. viride in biosorption process is little exploited [18].e present study in our laboratory is mainly aimed at knowing the application of T. viride for sequestration of Ni(II) from contaminated water systems involving kinetic and equilibrium.e selection of this biosorbent T. viride is based on (1) inexpensive, (2) easily available, (3) no toxic effects of its own, and (4) some information suggests that metal-bioaccumulation properties of T. viride [19].Hence, studies on the kinetic and equilibrium isotherm models have been studied, in order to systematically investigate the application of biomass, T. viride as biosorbent for the removal of nickel ions from water/industrial waste water.e optimum conditions for biosorption such as pH, initial metal ion concentration, biomass dosage, contact time, and equilibrium isotherm models in relation to the biosorption of Ni(II) onto T. viride have been investigated.In addition to this, the Ni(II) ion desorption studies have been performed over �ve sorption-desorption cycles to evaluate the sorbent T. viride for reusage.

Collection and Preparation of Biomass (Adsorbent)
. e fungal biomass was collected from Microbial Type Culture Collection (MTCC), Chandigarh, India.e biomass was prepared in the sabouraud broth (peptone 10.0, dextrose 40.0, streptomycin 0.03, and agar 20.0 g/L) by inoculating the 0.1 mL spore suspension/100 mL of water in the 250 mL �asks and incubated at room temperature for 5-7 days.Samples were washed several times using deionized water to remove adhesive materials such as extraneous salts and then dried in oven at 60 ∘ C for 48 h and powdered to uniform size using a mortar.

Reagents and Equipments.
A �ame atomic absorption spectrophotometer (Shimadzu AA-6300, Japan) with nickel hallow cathode lamp was used for determination of Ni(II) before and aer biosorption.Absorbance was measured at wavelength of 232 nm and spectral bandwidth was 0.2 nm.Fourier Transform Infrared (FT-IR) spectrometer (ermo-Nicolet FT-IR, Nicolet IR-200, USA) was used for IR spectral studies of dried biomass and Ni(II)-sorbed biomass in the range of 4000-400 cm −1 and Scanning Electron Microscopy (SEM, Model Evo15, Carl Zeiss, England) has been used to study the surface morphology of the biosorbent.

Results and Discussion
3.1.Characterization of Biomass.e FTIR spectra of free biomass and nickel sorbed biomass samples were showed in Figure 1.e spectra of free biomass (Figure 1(a)) has shown a broad and strong peak at 3354 cm −1 , which may be due to the overlapping of O-H and N-H stretching vibrations.e peak at 2924 cm −1 can be assigned to the -CH groups of an unloaded biomass sample.e peaks at 1642 and 1653 cm −1 may be attributed to asymmetric and symmetric stretching vibration of C=O groups, respectively.e spectrum of nickel sorbed biomass (Figure 1(b)) has revealed that the bands that have been observed at 3332, 1436, 1202, and 1079 cm −1 for free biomass are shied to 3354, 1449, 1244, and 1028 cm −1 .e signi�cant changes in the wave numbers of these speci�c peaks have suggested that amine, hydroxyl, C=O, and alcoholic C-O groups of biomass could be involved in the biosorption of nickel ion onto T. viride.
Figure 2 shows the morphology of T. viride before and aer biosorption of Ni(II).Before Ni(II) biosorption on T. viride shows adhesive and small particles (Figure 2(a)).It has been shown that the morphology changed to a corn �akelike structure aer Ni(II) biosorption onto T. viride biomass

Effect of PH. Biosorption of Ni(II) onto biomass of T.
viride as a function of initial pH has been shown in Figure 3.It has been observed that the biosorption capacity is increased from pH 2.0 to 4.5.Beyond pH 4.5, the biosorption has gradually decreased.At lower pH, the cell wall of T. viride becomes positively charged due to the increase in hydrogen ion concentration which is responsible for reduction in biosorption of Ni(II) ions on adsorption sites.In contrast, at higher pH (>4.5), the cell wall surface becomes more negatively charged when compared to surface negative charges at lower pH.At pH greater than 4.5, nickel ions start binding with OH − forming the insoluble nickel hydroxides that resulted in the reduction of biosorption.biosorption layer until saturation.e data obtained from the experiment has been further used to evaluate the kinetic parameters of the biosorption process.

Effect of Biosorbent Dose on Biosorption. e biosorbent dosage is an important parameter which determines the
3.5.Biosorption Kinetics.e mechanism of biosorption depends on the physical and chemical characteristics of the adsorbents as well as on the mass transfer process [20].e results of rate kinetics of Ni(II) biosorption onto T. viride biomass are analyzed using pseudo-�rst-order, pseudosecond-order, and intraparticle diffusion models.e conformity between experimental data and the model predicted values was expressed by correlation coefficients (R 2 ).e linear pseudo-�rst-order model [21] can be represented by the following equation: where   (mg/g) and   (mg/g) are the amounts of adsorbed metal on the sorbent at the equilibrium time and at any time t, respectively, and  1 is the rate constant of pseudo-�rstorder adsorption process (min −1 ).e experimental data was �tted to (1) and various parameters obtained for biosorption of Ni(II) onto T. viride with different initial concentrations together with correlation coefficients are given in Table 1.e correlation coefficients for the pseudo-�rst-order equation obtained at all the studied concentrations were low.is suggests that this biosorption system does not follow the �rstorder reaction.e kinetics of biosorption process may also be described by pseudo-second-order rate equation [22].e lineralized form of equation was given as follows: where  2 (g/(mg min)) is the equilibrium rate constant of pseudo-second-order biosorption.e pseudo-second-order equation parameters obtained for biosorption of Ni(II) onto T. viride with different initial concentrations together with correlation coefficients are given in Table 1.e biosorption results were analyzed using intraparticle diffusion model [23].is is represented as where   (mg/L) is the amount adsorbed at time t (min) and  id (mg/g min −0.5 ) is the rate constant of intraparticle diffusion.C is the value of intercept which gives an idea about the boundary layer thickness, that is, the larger intercept, the greater is the boundary effect.e Weber Morris plot for biosorption of Ni(II) is given in Figure 5. Based on the results, it can be concluded that both �lm diffusion and intraparticle diffusion are simultaneously operating during the biosorption of Ni(II) onto T. viride biomass.

Fitness of the
where  , and  , are the experimental biosorption capacities of metal ions (mg/g) at time t and the corresponding values that are obtained from the kinetic models.SSE values for all the kinetic models are calculated and summarized in Table 1.e lower SSE values of pseudo-second-order model indicate that the biosorption of Ni(II) on the T. viride biosorbent follows the pseudo-second-order kinetic model.

Biosorption Isotherms Models
. e equilibrium adsorption isotherm is of importance in the design of adsorption systems [24].e adsorption isotherms for Ni(II) adsorption onto T. viride biomass at the temperature of 20, 30, and 40 ∘ C are shown in Figures 6(a) and 6(b).e Langmuir treatment is based on the assumption that the maximum adsorption corresponds to a saturated monolayer of solute molecules on the adsorbent surface, that the energy of adsorption is constant, and there is no transmigration of adsorbate in the plane of the surface [25].It is represented by where   is the equilibrium metal ion concentration on the sorbent (mg/g),   is the equilibrium metal ion concentration in the solution (mg/L),   is the monolayer sorption capacity of the sorbent (mg/g), and   is the Langmuir sorption constant (L/mg) related to the free energy of sorption.Figure 6(a) shows the Langmuir plots at different temperatures and the constants   and   are tabulated in Table 2. On the other hand, Table 3 presents the comparison of biosorption capacity (mg/g) of T. viride for Ni(II) ions with that of various biosorbents reported in the literature [26][27][28].e general form of Freundlich is given as follows: where   is a constant related to the biosorption capacity and 1/n is an empirical parameter related to the biosorption intensity, which varies with the heterogeneity of the material.Figure 6(b) shows the Freundlich plots at different temperatures and the constant   and 1/n are tabulated in Table 2. e best �t biosorption isotherm model is con�rmed by the correlation coefficients ( 2 ) and the chi-square ( 2 ) tests.e equation for evaluating the best �t model is to be written as where q  is the experimental data of the equilibrium capacity (mg/g) and q , is equilibrium capacity obtained by calculating from the model (mg/g). 2 will be a small number if the data from the model are similar to the experimental data, while  2 will be a bigger number if they differ.us, it is also necessary to analyse the data set using the nonlinear  2 test to con�rm the best-�t isotherm for the biosorption process and the  2 values are given in Table 2. e  2 values of both isotherms are comparable and hence the adsorption of metal ions follows both Freundlich and Langmuir isotherms and better �t to Langmuir as its  2 value is less than that of the Freundlich model.(0.01-0.4 M) were used to desorb the Ni(II)-T.viride complex.e results of the present study indicate that the addition of acid at lower concentration 0.01 M HNO 3 desorbs the nickel from the complex and >55% adsorption was observed at 0.05 M HNO 3 .e maximum desorption (>98%) of nickel from the complex occurs at >0.25 M HNO 3 .

Recovery of Ni(II) by Adsorption-Desorption Cycle.
In order to evaluate the reutilization of the T. viride, the biosorption-desorption cycles are repeated �ve times by treating the used biosorbent with 0.25 M HNO 3 .e desorption efficiency of 99.77% of Ni(II) was obtained by using 0.25 M HNO 3 in the �rst cycle and is, therefore, suitable for regeneration of biosorbent.ere was a gradual decrease of

Conclusion
is study is focused on the biosorption of Ni(II) ion onto T. viride biomass from aqueous solution.e operating parameters, pH of solution, biomass dosage, contact time, initial metal ion concentration, and temperature are effective on the biosorption efficiency of Ni(II).e biosorption capacity of T. viride biomass has been found to be 47.6 mg/g for Ni(II).Langmuir model has �tted the equilibrium data better than the Freundlich isotherm.e kinetic data has illustrated that pseudo-second-order model is more suitable than a pseudo-�rst-order model based on the lower SSE and correlation coefficients that are greater than 0.99.T. viride can be used for 5 cycles by regenerating with 0.25 M HNO 3 .Further, it can be evaluated as an alternative biosorbent to treat wastewater containing Ni(II) ion over the classical physicochemical methods.Hence, T. viride can be used as an effective, low-cost biosorbent for potential removal of heavy toxic metal Ni(II) from aqueous media.e signi�cant advantage of T. viride is reusage of it when compared to other methods using different types of fungi for removal of Ni(II) from water media.

F 1 :
FTIR spectra of T. viride biomass before adsorption (a) and aer adsorption of Nickel (b).

F 2 :
SEM micrographs of T. viride biomass surface, (a) before adsorption of Ni(II) ions and (b) aer adsorption of Ni(II) ions.(Figure 2(b)).It can be seen that the surface modi�cations occurred by reducing the irregularity, aer binding of Ni(II) ions onto the surface T. viride biomass.

F 3 :F 4 :
Effect of pH on the biosorption of Ni(II) onto T. viride biomass.Effect of biosorbent dosage level on the biosorption of Ni(II) T. viride biomass.capacity of a biosorbent for a given initial concentration.e biosorption of Ni(II) ion as a function of the biosorbent dosage of 0.1 g to 0.7 g has been investigated and the results are shown in Figure4.e percentage of biosorption has increased with the increase of biosorbent dose up to 0.5 g/0.1 L. At the initial concentration of 100 mg/L of Ni(II), the maximum percentage removal was 92.3% and remained constant at >0.5 g/0.1 L. erefore, the optimum biosorbent dosage was taken as 0.5 g for further experiments to determine the effect of contact time, biosorption kinetics, and biosorption isotherm models.

F 5 :
Weber and  Morris plots for the biosorption of Ni(II) T. viride biomass.

3. 8 .F 6 :
Desorption Experiment.In addition to biosorption studies, desorption processes have equal importance due to the reusage of biomass material.Desorption mainly depends upon (a) type of eluents and (b) biomass material used.In the present study, HNO 3 solution was used as the eluent to remove Ni(II) from T. viride.Different concentrations (a) Langmuir isotherm plots for the biosorption of Ni(II) T. viride biomass at different temperatures.(b) Freundlich isotherm plots for the biosorption of Ni(II) T. viride biomass at different temperatures.
3.4.Effect of Contact Time.e biosorption capacity of T.viride towards Ni(II) was investigated at different initial concentrations and �xed amount of fungi at different time intervals.e efficacy of biosorption increases with agitation time and reached equilibrium about 180 min for all the experimental concentrations performed.e rate of the uptake of metal ions was rapid in the early stages as expected, then the equilibrium was attained due to continuous formation of the T 1: Kinetic parameters for biosorption of Ni(II) by T. viride biomass.
Biosorption Kinetic Models.e values of rate constants and correlation coefficients for each model were shown in Table 1.e best �t among the kinetic models is assessed by the squared sum of error (SSE) values.It is assumed that the model which gives the lower SSE values is the best model for metal ion sorption on T. viride.e SSE values are calculated by the following equation: T 2: Langmuir and Freundlich isotherm parameters for the biosorption of Ni(II) on T.viride biomass at different temperatures.Ni(II) biosorption on T. viride with an increase the number of desorption cycles.A�er a sequence of �ve cycles, it was observed that the Ni(II) uptake capacity of the T. viride has been reduced from 98.15% to 95.13%.e desorption efficiency more than 98% recovery of Ni(II) was observed in each cycle of all the �ve consecutive desorption cycles.e results indicate that the T. viride can be used repeatedly in the adsorption-desorption cycles.